1. Field
The present invention relates to elevators and to methods for preventing uncontrolled slackening of the hoisting ropes and/or uncontrolled movement of a compensating device in an elevator.
2. Description of Related Art
One of the objectives in elevator development work is to achieve an efficient and economical utilization of building space. In recent years, this development work has produced various elevator solutions without machine room, among other things. Good examples of elevators without machine room are disclosed in specifications EP 0 631 967 (A1) and EP 0 631 968. The elevators according to these specifications are fairly efficient in respect of space utilization as they have made it possible to eliminate the space needed for the machine room in the building without a need to enlarge the elevator shaft. The machine used in the elevators according to these specifications is compact in at least one direction, but in other directions it may be much larger than conventional elevator machines.
In these basically good elevator solutions, the space and placement of the hoisting machine limits the freedom of choice in elevator lay-out solutions. The arrangements for the passage of the hoisting ropes require space. The space required by the elevator car itself on its track, and likewise the space needed for the counterweight, can not be easily reduced, at least at a reasonable cost and without compromising on the performance and quality of operation of the elevator. In a traction sheave elevator without machine room, installing the hoisting machine in the elevator shaft, especially in the case of solutions with machine above, is often difficult because the hoisting machine is a fairly heavy and large object. Especially in elevators for larger loads, speeds and/or hoisting heights, the size and weight of the machine are a problem in respect of installation, even so much so that the required machine size and weight have in practice limited the scope of application of the concept of elevator without machine room, or at least retarded the introduction of said concept in larger elevators. The space available in the elevator shaft in elevator modernization projects has often limited the scope of application of the concept of elevator without machine room. Often, especially in cases of modernization or replacement of hydraulic elevators, it has not been practical to apply a roped elevator solution without machine room, due to insufficient space in the elevator shaft especially in a situation where no counterweight has been used in the hydraulic elevator solution to be modernized/replaced. The drawbacks of elevators provided with a counterweight include the cost of the counterweight and the space required for the counterweight in the elevator shaft. Drum-driven elevators, which at present are quite rare, have the disadvantages of heavy and complicated hoisting machines and their high power and/or torque requirements. Prior-art elevator solutions without counterweight are exotic and no appropriate solutions are known. So far, it has not been technically or economically reasonable to make elevators without counterweight. One solution like this is disclosed in specification WO9806655. A recent international patent application discloses a feasible solution. In prior-art elevator solutions without counterweight, the tensioning of the hoisting rope is implemented using a weight or spring, and that is not an attractive approach to implementing the tensioning of the hoisting rope. Another problem with elevators without counterweight, when long ropes are used e.g. due to a large hoisting height or large suspension ratios used, the compensation of rope elongations and at the same time, due to rope elongations, the friction between the traction sheave and the hoisting ropes is insufficient for the operation of the elevator. A further problem is how to ensure the compensation of rope elongations and the operating reliability of the compensating device. In the case of elevators without counterweight, ensuring a sufficient safety space in the shaft is a problem. Another problem in an elevator without counterweight is uncontrolled slackening of the hoisting ropes and a risk of the ropes getting tangled, especially in a situation where the elevator car is driven onto the buffers.